Infusion systems that are designed in the form of a multichannel dispensing system for dispensing different volumes of solutions are used to dispense medical substances. Individual dispensing syringes, which are filled with the solutions selected by the user, are inserted in such systems into syringe holders, wherein the pistons of the dispensing syringes are actuated by a motor drive in order to pump the individual solutions into an infusion line. A central control unit of the multichannel dispensing system monitors the rate of dispensing of the individual solution.
The drawback of the prior-art multichannel dispensing system is that the dispensing syringes are disposable articles for hygienic reasons and must be disposed of The motor drives, which actuate the pistons, must operate with high precision and are therefore expensive. Due to the limited overall size of multichannel dispensing systems, the volume of the dispensing syringes is limited. Emptied dispensing syringes must therefore be frequently removed and replaced with new ones. In addition, the dispensing rates of the solutions affect each other and high time constants must be accepted in case of a change of the dispensing rates. A multichannel dispensing system of the said type has become known from DE 43 20 365 A1.
Microdispensing devices, which are based on the direct displacement of the solution to be dispensed, are known from other fields of application. An essential component of microdispensing devices is a pressure chamber, which is partially limited by a displacer in the form of a flexible membrane. By actuating the displacer, the solution to be dispensed is drawn up from a reservoir and then ejected from the pressure chamber via a discharge opening. The suction phase is controlled now such that a small change in the volume of the pressure chamber per unit of time is set.
In contrast, a great change in volume per unit of time is generated during the phase of dispensing in order to dispense a defined volume of solution. Depending on the viscosity and the surface tension, solutions can be dispensed in the range between 0.01 μL and 0.1 μL with some microdispensing devices. A microdispensing device of this type has become known from DE 198 02 368 C1.
Certain medical substances, for example, antibiotics, have only a limited shelf life in the liquid form. Dry powdered drug dispensing devices, with which very fine particles of a powdered drug can be made available in predetermined doses, are known for dispensing powdered drugs. A device of this type has become known from EP 826 386 B1. The drug is delivered to the patient via the respiratory tract with the prior-art dry powdered drug dispensing device.
However, the prior-art microdispensing devices and the dry powdered drug dispensing devices are not suitable for delivering the drugs to a patient intravenously.